The invention relates to a method for testing a cutting-edge geometry of a rotatably drivable tool and a device for performing the method according to the invention. In particular, the invention relates to the testing of a cutting-edge geometry of a tool for the purpose of breakage and wear monitoring by means of a measuring beam.
The use of measuring systems to test rotatably drivable tools using a measuring beam, in particular an optical measuring beam is known. Thus, DE 42 38 504 describes a method that measures the length and the diameter of a tool and also concentricity errors using a thin laser beam. In this way, not only can the setting of the tool be checked, but also wear or a break in the tool can be detected. In this procedure, the tool is presented to an optical measuring plane perpendicular to the measuring plane. The measuring system outputs a signal that indicates whether the tool has entered the measuring plane. When the tool enters, its relative position is determined with respect to the measuring plane in order to calculate the dimensions of the tool using reference points. In order, in addition, to determine the concentricity and the diameter of the tool, the rotating tool is also fed parallel to the measuring plane.
In order to avoid impairments of the measuring operation as a result of contaminants in the air in a measuring region of an optical measuring system, in accordance with DE 42 44 869, a signal that indicates the entry of a tool into the measuring plane is generated only if a drastic signal decrease is detected in a laser beam used as measuring beam. In addition, comparison values are recorded by the measuring system that serve as reference values for individual measuring operations and are intended to reduce interference effects that impair the measuring operation.
Furthermore, DE 32 18 754 discloses a method for measuring the length of a rotatably drivable tool. In this method, the tool passes an optical measuring device, the position of the tool being determined when the tool tip passes through a measuring plane of the optical measuring device. The length of the tool can be calculated by comparing the measured position with a standard position of the tool. In this way, it is also possible to determine whether the tool is broken.
During the industrial application of these described methods, it has emerged that faulty or unsatisfactory measurements occur as a result of contaminants, e.g. due to coolants or metal chips, in the measuring regions of the optical measuring systems used. Furthermore, the optical measuring systems used have to be re-adjusted as a function of the tools used and also their rotational speed has to be re-adjusted for the particular application case. In addition, none of these known methods makes possible a check of the individual cutting edges of a tool or also a complete check of the geometry of a tool.
DE 39 05 949 A1 discloses a measuring system for testing a cutting-edge geometry in which occlusions of a measuring beam due to obstacles in its propagation path are detected and evaluated. No provision is made therein to take account of standard time instants and detection time instants.
In accordance with DE 692 23 544 T2, interferences in the optical measurement of the profile of an object are eliminated in that the optical scanning of the object by means of a laser beam is restricted to predetermined time intervals. For this purpose, the laser beam is allowed to emit light in an illumination time interval, whereas the laser beam is switched off in a switched-off time interval. For this purpose, a read-out device for receiving the laser beam is operated synchronously in order to repeat alternately a synchronous read-out scanning operation of light-receiving elements.
DD 245 481 A1 discloses a method and an arrangement for determining photoelectrically the position of edges on rotating specimens with respect to their axis of rotation. In this method, during a first revolution, that rotation position of the specimen relative to the photoreceiver in which a specified edge of the specimen is detected by a photoreceiver is determined by means of an optical measuring method. During further revolutions of the specimen, only those photoreceiver signals that are detected in the previously determined rotation position of the specimen are evaluated by means of a high-resolution, slow method.
From U.S. Pat. No. 3,900,738, U.S. Pat. No. 3,817,647, JP(A) 0 221 20 45 and U.S. Pat. No. 4,667,113, it is known, for the purpose of testing a cutting-edge geometry of a rotatably drivable tool, to move a region to be tested of a tool that is being rotated at a specified rotational speed into a measuring range defined by a measuring beam and to detect signals that indicate when and if the measuring beam is instant on the region to be tested or is interrupted by it.
In accordance with DE 197 20 176 C1, to eliminate interfering signals in the case of a light barrier, light pulses incident on a receiver of the light barrier are evaluated only during specified time intervals whose time period is matched to the length of the time intervals within which light pulse sequences are emitted by a transmitter of the light barrier.
It is therefore the object of the invention to eliminate interference effects in a measuring plane of a measuring system during the testing of a rotatably drivable tool.
In order to make possible a desired machining quality with a rotatably drivable tool, it is necessary to ensure that the tools used have certain properties. Said properties include, inter alia, the positioning of a tool in a suitable holding device of the tool machine and also the geometry of the tool itself. With the aid of the method according to the invention, it becomes possible to check a rotatably drivable tool in regard to its actual shape. For this purpose, a region to be tested is defined on the tool, for example the region of the cutting edge of the tool. The tool is rotated at a desired rotational speed and is introduced into a measuring range that is defined by a measuring beam. As a result of the rotation of the tool, the measuring beam is able to strike that region of the tool to be tested, but it is also possible that the measuring beam does not strike the region to be tested. Beside this interaction with the region to be tested, interactions between the measuring beam and other media or substances situated in the measuring range may also occur, for example with drops of coolant or metal chips. In order to test the tool, the interactions of the measuring beam with the region to be tested are detected. In this connection, it is necessary to avoid interactions between the measuring beam and the other substances or media that result in spurious measurements.
According to the invention this is avoided in that the detection takes place only during time intervals that comprise time instants at which it is to be expected that the region to be tested enters the measuring beam during the rotation. Such time instants are determined using a specified pitch, denoted below as standard pitch, of a reference tool corresponding to the tool to be tested. These time instants determined are denoted below as standard time instants. The detection is then performed during chosen detection intervals that each contain a standard time instant in order to check, on the basis of optical interactions that occur or do not occur, whether the tool has the standard pitch or is damaged.
In this connection, provision is made that the detection time intervals are chosen in such a way that they do not overlap in time. Furthermore, the detection time intervals can be chosen in such a way that they comprise the corresponding standard time instant symmetrically.
Tools that are used as reference tools for the tools to be tested comprise real tools whose dimensions comply with the desired dimensions for the tool to be tested, for example undamaged or new tools, but also so-called xe2x80x9cvirtual toolsxe2x80x9d. Here xe2x80x9cvirtual toolsxe2x80x9d are not to be understood as the tools in the actual sense, but the formal description of the dimensions of the tool geometry. The formal description may take place, for example, through mathematical formulae and/or data. Since, as described later below, the invention may also comprise programmable components, the use is to be preferred of xe2x80x9cvirtualxe2x80x9d reference tools in the form of data that are stored and processed, for example, in a computer-aided manner.
The size of the chosen detection time intervals is to be chosen as small as possible as a function of the particular application case in order to restrict the detection to a time range that starts as short a time as possible before the standard time instant and ends as short a time as possible thereafter. In this way, the reliability of the tool testing is increased. Preferably, the detection time intervals are chosen so small that they contain the appropriate standard time instant only with a slight time excess.
Preferably, the standard time instants and/or detection time intervals are determined as a function of the rotational speed of the tool. In addition, it is advantageous if the standard time instants and/or detection time intervals are determined taking into account the standard pitch.
In a preferred embodiment of the invention, the detection time instants that are necessary to synchronize the detection with the rotating tool to be tested are determined by determining a standard time interval as a function of the standard pitch. Said standard time interval indicates the time spacing between two time instants at which it is to be expected that various regions of that region of the tool to be tested enter the measuring beam. The signals are then detected that indicate interactions of the measuring beam with obstacles in its propagation path, the detection being performed until at least two consecutive such signals are detected whose time spacing corresponds to the predetermined standard time interval.
In addition, it is possible to start the detection after a last signal detected in the standard time interval, the time spacing of the standard time instants corresponding to the standard time interval.
In order to test tools of irregular geometry, it is possible to define a sequence of standard time intervals as a function of a standard pitch of the tool that is in this case an irregular pitch. Subsequently, the signals that indicate the interactions of the measuring beam with obstacles in its propagation path are detected until at least two consecutive signals are detected whose time spacing corresponds to one of the standard time intervals of the defined sequence. Preferably, in the above-described embodiments of the invention, the detection used for synchronization is performed continuously.
It is consequently made possible to start the detection according to the invention after a last signal detected in one of the standard time intervals. According to the invention, the detection then takes place at the standard time instants whose time spacings in this case have a sequence that corresponds to the defined sequence of standard time intervals.
Furthermore, it is to be preferred that the tool to be tested is positioned in the measuring range by detecting an entry of the envelope surface of the region to be tested, which envelope surface results from the rotation of the tool, using the measuring beam.
It is also possible to generate a result signal in response to the detection according to the invention in order to indicate a total result of the testing of the tool. It is thus possible to generate a result signal that indicates a successful summary testing of the tool if a number of the signals detected at the standard time instants is above a predetermined number or the predetermined number is reached exactly.
In a further embodiment of the invention, the determination of the standard time instants is performed again if the number of the signals detected at the standard time instants is below the predetermined number. In addition, a result signal can be generated that indicates an unsuccessful testing of the tool if the number of the signals detected at the standard time instants is below the predetermined number.
In addition, it is possible to define a detection time period for which the detection is performed at the standard time instants.
In addition, a determination time period may be chosen that indicates the space of time in which the determination of the standard time instants is performed. Thus, a result signal can be generated that indicates an unsuccessful summary testing of the tool if the determination of the standard time instants is performed for longer than the chosen determination time period.
The detection time period and/or the determination time period may be determined in this connection as a function of the rotation of the tool and/or as a function of the standard pitch.
In order to test not only an individual region of the tool, but to test a plurality of regions of the tool or the entire tool, the method according to the invention is repeated after completion of the test. In this case, after completion of the testing of a region of the tool, movement is performed relative to the measuring range in such a way that the envelope surface, produced by the rotation, of a further region to be tested enters the measuring range or is situated in the latter. The subsequent test steps according to the invention are then performed again. This procedure is repeated for every region to be tested, every further region of the tool to be tested preferably being adjacent to the previously tested region.
As an alternative to this testing of a plurality of regions or in combination therewith, a plurality of adjacent regions, fairly large continuous regions of the tool or the entire tool can be tested if, in addition to the rotation of the tool, the latter is simultaneously moved relative to the measuring range, for example perpendicularly to the measuring range so that an envelope surface, produced by the rotation and the relative movement of the tool, for the adjacent regions to be tested or of the continuous region to be tested enters the measuring range or is situated in the latter.
To execute the method according to the invention, a measuring system is used that has a transmitter for emitting a measuring beam, a receiver for receiving the measuring beam and for outputting signals that indicate a received measuring beam, an evaluation unit connected to the receiver for receiving signals outputted by the receiver and for generating signals that indicate the interactions of the measuring beam with obstacles in its propagation path as a function of the received signals and a control unit for controlling the measuring system.
In an embodiment of the invention, the evaluation unit evaluates the signals of the receiver only during chosen evaluation time intervals in which standard time instants are situated at which a region, corresponding to the region to be tested, of a reference tool having a standard pitch enters the measurement beam.
In another embodiment, the receiver receives the measuring beam only during chosen receiving time intervals in which in each case only one standard time instant is situated at which a region, corresponding to the region to be tested, of a reference tool having a standard pitch enters the measuring beam.
In a further embodiment, the transmitter transmits the measuring beam only during chosen transmitting time intervals in which a standard time instant is situated in each case at which a region, corresponding to the region to be tested, of a reference tool having a standard pitch enters the measuring beam.
Further embodiments of the invention emerge as combinations of individual or a plurality of the abovementioned embodiments of the measuring system according to the invention.
In order to achieve a compact design, the control unit and/or the evaluation unit may be incorporated in the transmitter and/or the receiver.
In order to be able to use the measuring system according to the invention flexibly, the evaluation unit and/or the control unit should be programmable.
In addition, it is desirable to connect the measuring system or, preferably, the control unit to a machine or its control, respectively, that rotates the tool to be tested in order, for example, to exchange items of information relating to the rotational speed, shape of the tool, desired machining operations and their precision and also tests of the tool performed with the measuring system according to the invention.
The measuring beam can be any desired beam that can enter into interaction with a tool to be tested and with other obstacles in its propagation path and which makes possible a detection of the interactions with a suitable receiver or detector. Thus, the measuring beam may be an optical measuring beam, an electromagnetic measuring beam, a corpuscular measuring beam or a combination of said measuring beams. In view of the available components that are necessary to generate, emit and detect measuring beams, and also their complexity and cost, the measuring beam is preferably an optical measuring beam and, in particular, a laser light beam.
Since in the method according to the invention, the testing of the tool takes place essentially at the so-called standard time instants at which it is to be expected that that region of the tool to be tested enters the measuring beam, spurious measurements are avoided that are to be attributed to interaction and that are not interactions of the measuring beam with the region to be tested.
Furthermore, the invention makes it possible, as a result of the use of programmable control and evaluation units, to adapt flexibly the testing of a tool of a machine tool in an application-specific way to the respective tool used and the respective machine tool used. Thus, tools can be tested that rotate at different rotational speeds and that have the most varied, and even irregular geometries and pitches.